As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are commercially available in sealed packages made of a packaging material that has previously been sterilised.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multi-layer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or of mineral-filled polypropylene material, and a number of layers of heat-seal plastic material, e.g. polyethylene film, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas- and light-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH), which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
As is known, packages of this sort are produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution. Once sterilization is completed, the sterilization agent is removed from the surfaces of the packaging material, e.g. evaporated by heating. The web of packaging material sterilized in this manner is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed at equally spaced cross sections, along which it is eventually cut to form the packs. These pillow-shaped packs are then folded mechanically to form finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles. These packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
Once formed, the aforementioned packages may undergo further processing, such as applying a reclosable opening device to protect the food product inside the package from contact with external agents, and to enable the product to be poured out.
At present, the most commonly marketed opening devices comprise a frame defining a pour opening and fitted about a pierceable or tear-off portion of a top wall of the package, and a cap hinged or screwed to the frame, which is removable to open the package; as an alternative, the use of different types of opening devices, such as slidingly operated opening devices, are also known.
The pierceable portion of the package may be defined e.g. by a so-called “prelaminated” hole, i.e. a hole formed in the base layer of the packaging material before coupling this layer with the layer of barrier material, which is therefore intact and closes the hole itself, thus ensuring hermetic sealing and asepsis although resulting easy to perforate.
In the case of aseptic packaging machines, the opening devices are normally fitted directly to the packages, after they are formed, in units placed on the production line downstream from the packaging machine.
The aforementioned units substantially comprise a gluing assembly within which a fastening portion of the opening devices is coated with a layer of adhesive, an application assembly within which the opening devices are applied on respective packages and a pressure assembly within which the opening devices are pressed on the respective packages for a time required to allow the cooling of the adhesive and the complete adhesion of each opening device on the corresponding package.
Application assemblies are known, e.g. from patent EP1813533, comprising a first linear step conveyor adapted to feed a sequence of packages along a first rectilinear path, a second linear step conveyor adapted to feed a sequence of opening devices along a second rectilinear path, and a rotating carousel conveyor which is also step operated, which is adapted to carry the opening devices from a withdrawal station coinciding with a stop station of the second conveyor to an application station of the opening devices on the respective packages coinciding with a stop station of the first conveyor.
Each gripping member is movably constrained to the carousel conveyor radially to a rotation axis of the carousel conveyor between a retracted position and an advanced position.
More specifically, each gripping member is placed at a maximum and at a minimum radial distance from the axis of the carousel conveyor respectively in the corresponding advanced and retracted position.
Each gripping member is arranged in the advanced position when it withdraws the opening device from the first conveyor, it is advanced in the retracted position from the carousel conveyor, and it is arranged in the advanced position when it applies the opening device onto the corresponding package.
Specifically, each gripping member applies the opening device on the corresponding package in a direction perpendicular to a top wall of the package and radial with respect to the axis of the carousel conveyor, so as to arrange the flat fastening area of the opening device parallel to and in contact with the top wall of the package itself.
Although more reliable and effective, the disclosed application assemblies may further be improved.
Specifically, a need is felt for maximum flexibility as regards the approaching trajectory of the gripping means to the packages advancing along the first path during the step of applying opening devices onto the respective packages.
This flexibility is especially advantageous when the fastening area of the opening devices on the corresponding packages does not lie on a single plane. Indeed, in this case advancing the gripping member exclusively in a radial direction towards the advancing package would not arrange the aforementioned fastening area totally resting against the wall of the package.
The adhesive could therefore escape from the fastening area and the gluing efficiency of the opening devices on the corresponding packages could therefore be compromised.
This need is especially felt in relation to opening devices fitted with a frame straddling an edge between a first and a second wall of the package, e.g. the top wall and the top end portion of a side wall of the package, and comprising a first and second portion forming an angle therebetween and intended to be glued respectively to the aforementioned first and second wall at respective fastening areas lying on respective reciprocally inclined planes.